1. Field of the Invention
The present invention relates to a dynamo-electric machine rotor and, more particularly, to a rotor coil cooling structure configured to feed coolant gas between adjacent coil ends.
2. Related Art
A dynamo-electric machine such as a turbine generator is composed of a hollow cylindrical stator and a cylindrical rotor with a diameter somewhat smaller than that of the hollow portion which are concentrically arranged with an air gap between them. In each of the stator and rotor, conductive bars, i.e., so-called coils of copper or the like are arranged in the axial direction of core slots. When the rotor is rotated while its coils are energized, current is induced on the stator side.
At this time, since high heat is generated in the stator and rotor due to an electrical loss or the like, special cooling is required. The stator and rotor are forcedly cooled by feeding coolant gas into the machine by means of, e.g., placement of a fan in the rotor. In particular, the cooling performance of rotor coils which use rotational centrifugal force as the driving force for coolant gas is an important factor which influences the performance and build of a generator.
FIG. 29 shows a sectional view of ends of conventional rotor coils. FIG. 30 shows a horizontally spread-out view of the ends of the rotor coils. As shown in FIGS. 29 and 30, a conventional dynamo-electric machine rotor has a ventilating groove 10A in the longitudinal direction of each of rotor coils 10 and cools the rotor coils 10 by feeding coolant gas A through the grooves.
The rotor coils 10 of stacked turns are fitted into slots which are circumferentially formed at predetermined intervals in a core 30 integrated with a rotor shaft 13 to form multiple nested rings. Ends 10E of the rotor coils 10 which are located outside an end of the rotor core are held by an retaining ring 34 and an retaining ring support 35 against rotational centrifugal force. As shown in FIG. 29, the ends 10E of the rotor coils 10, whose outer side is surrounded by the retaining ring 34, are held at predetermined intervals while a spacer 20 shown in FIG. 31 is arranged between each two adjacent coils. An insulating cylinder 40 is inserted to maintain electrical insulation between the outermost portion of the rotor coil ends 10E and the retaining ring 34.
Since field current for energization flows through the rotor coils 10, electric heat is generated, and the temperatures of the coils rise. In addition to the insulating cylinder 40, insulators (not shown) are inserted between adjacent stacked turns of each rotor coil and between the core slots and the rotor coils, and the upper temperature limit is defined on the basis of the heat-proof temperatures of the insulators and the like.
As described above, coolant gas passes through an air gap between the rotor shaft 13 and the retaining ring support 35 and is guided to the retaining ring 34, and part thereof is guided to a ventilating channel in each rotor coil 10 from a ventilating inlet formed in a side of the rotor coil 10. The coolant gas guided into the ventilating channel of the rotor coil 10 flows through the ventilating channel in the longitudinal direction of the rotor coil 10, thereby cooling the rotor coil 10. After that, the coolant gas passes through a radial duct 14 in the core and is discharged to the outer periphery of the rotor.
In addition to this, a method is disclosed in National Publication of International Patent Application No. 2000-508508 or the like in which no ventilating groove is formed in a coil itself, a ventilating groove is formed in each side of a spacer arranged between coils, and partition plates are provided all around the inner periphery of rotor coils, thereby enhancing cooling between coils. As shown in FIG. 32, each partition plate has an opening near the border between a coil linear portion 12 and a coil circular portion 11, and cooling is performed by causing coolant gas to pass in the directions indicated by arrows.
However, in the cooling method, in which each rotor coil has the ventilating groove 10A, coolant gas flows in the longitudinal direction. Accordingly, the temperature of the coolant gas becomes higher toward the downstream side, and the temperature of one of the coils which is circumferentially distant from a magnetic pole center and is near the core end is higher than that of one near the magnetic pole center where an inlet 10B for coolant gas is located, as shown in FIG. 30. Also, the more distant from the center one of the rotor coils is, the longer the rotor coil is. Accordingly, the temperature of an outer coil is higher than that of an inner coil, and it is highly possible that the distribution of temperature becomes wider in the axial direction and circumferential direction of the rotor coils. FIG. 33 shows an example of a set of temperature distributions.
The temperatures of rotor coils are strictly limited by the upper temperature limit for a member used as an insulator for the coils. If the temperature is locally high at a part of a coil, there arises the need to limit field current and suppress the amount of heat generated even when the temperatures at other parts are sufficiently lower than the upper temperature limit. Accordingly, it is impossible to turn up a dynamo-electric machine. Also, if temperatures differ among coils of a large number of turns, shaft vibration occurs due to imbalance in thermal expansion among the rotor coils, and the reliability of the generator decreases.
On the other hand, in a method in which a ventilating groove is formed in each side of a spacer arranged between coils, and partition plates are provided below rotor coils outside a rotor core, thereby performing cooling between the coils, as in National Publication of International Patent Application No. 2000-508508, the flow rate of coolant gas passing through a ventilating groove in a spacer is lower than that of coolant as passing through a ventilating groove in a coil, and thus the cooling performance is lower. Also, the method requires components for the partition plates and man-hours for assembling them, thus leading to cost increase.
A rotor coil of a turbine generator is formed by stacking a plurality of turns each generally having a thickness of about several mm. Since the thin turns are not tightly bound nor held by one another, they each thermally stretch with an increase in temperature during the operation of the generator. For this reason, it is desirable for a spacer to be in contact with all turns at longitudinally identical positions, if possible.
However, in the invention described in National Publication of International Patent Application No. 2000-508508, a zigzag ventilating groove is formed in each side of a spacer. Accordingly, surfaces on a side of each spacer which are in contact with a coil are staggered and are discontinuous in the longitudinal direction. For this reason, the coil end holding power in the technique described in National Publication of International Patent Application No. 2000-508508 is lower than a rotor which uses a plain spacer without a ventilating groove in each side.